Advanced Higher Chemistry 2009 Watch

Meteorshower
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#101
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#101
Well I don't have the question but

delta G = delta H - Temperature x delta S
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Dan11
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#102
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#102
Help with 2004 q12 (b)?

thanks
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Meteorshower
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#103
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#103
(Original post by Dan11)
Help with 2004 q12 (b)?

thanks
All of it or a specific part?
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Kieran578
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#104
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#104
2008, Q2a - no idea how to do these type of Qs - is it just something you should know?
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Meteorshower
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#105
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#105
You just need to know.

The higher wavelength end is red, the lower is violet/blue and this is supposed to be the middle so green.

If you have difficulty remembering that green is the middle, Richard of york gave battle in vain is a helpful mnemonic.

I'm off, to bed, Far too tired.
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Dan11
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#106
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#106
The first part please. Calculating the mass of C,H and O.
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Meteorshower
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#107
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#107
(Original post by Dan11)
The first part please. Calculating the mass of C,H and O.
Ok, i'll postpone sleep just for you :p:

You know that all the carbon of x is now in the form of carbon dioxide.
You know that all the hydrogen of x is now in the form of water.

12/44 is the ratio of carbon in carbon dioxide, so you times that by 0.478 to get the mass of carbon from x

Do the same for water except obviously you need to use 2/18

Now subtract the mass of carbon and hydrogen from the total mass of x and since there are no other possible elements in X this will be the mass of oxygen.

Then divide all your masses by their relative formula masses to get the amount of moles for each, and you should be able to get your empirical formula from there.


Now i'm really off to sleep :p:
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Kieran578
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#108
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#108
(Original post by Meteorshower)
You just need to know.

The higher wavelength end is red, the lower is violet/blue and this is supposed to be the middle so green.

If you have difficulty remembering that green is the middle, Richard of york gave battle in vain is a helpful mnemonic.

I'm off, to bed, Far too tired.

good man...... ROYGBV roy - g - bv is my way.....
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Kieran578
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#109
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#109
By the way, I had a dream a few weeks ago that the PPA would be on kinetics - just writing it down so that if it comes up I have proof of my psychic powers
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abstraction98
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#110
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#110
(Original post by Kieran578)
good man...... ROYGBV roy - g - bv is my way.....
ROY - G - BIV

(Original post by Kieran578)
By the way, I had a dream a few weeks ago that the PPA would be on kinetics - just writing it down so that if it comes up I have proof of my psychic powers
Likely to be two or three. Personally, I'm betting on gravimetric analysis - never come up in recent years.
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Ellesmith
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#111
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#111
Could anybody please enlighten me on mass spectrometry? For example 2004 q12 c and d. I have never got my head round it..
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Aiex
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#112
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#112
question about partition coefficients, when you're working it out, which concentration goes on top and which below?

e.g. for aques/cyclohexane, cycloe is above aqueous, what about other solvents?
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abstraction98
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#113
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#113
(Original post by Aiex)
question about partition coefficients, when you're working it out, which concentration goes on top and which below?

e.g. for aques/cyclohexane, cycloe is above aqueous, what about other solvents?
Good question. I would always put the one with least density on the top. In practice this is nearly always the organic solvent, but I too am confused with a definitive method.
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Dan11
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#114
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#114
HOw would a q like this be done:

A buffer solution is made by dissolving 2.96g of propanoic acid and 7.68g of sodium propanoate in water. Calculate the pH of the buffer.

I know that u need to use the equation, ut how do u get the conc. of both the parts?.....
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abstraction98
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#115
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(Original post by Dan11)
HOw would a q like this be done:

A buffer solution is made by dissolving 2.96g of propanoic acid and 7.68g of sodium propanoate in water. Calculate the pH of the buffer.

I know that u need to use the equation, ut how do u get the conc. of both the parts?.....
Let volume = v and find the concentrations with that variable.

See what happens. (It will cancel out in your acid/salt bit)

Clever eh?
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phpurvis
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#116
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#116
(Original post by Dan11)
HOw would a q like this be done:

A buffer solution is made by dissolving 2.96g of propanoic acid and 7.68g of sodium propanoate in water. Calculate the pH of the buffer.

I know that u need to use the equation, ut how do u get the conc. of both the parts?.....
Need to know how much water they're dissolved in methinks.

Find out the number of moles of each substance by finding their relative formula masses first.

Then you'd use C = N/V to find the concentration, dividing the number of moles by the volume of water.

Once you have the concentration of each, use the following equation:

pH = pKa - log[acid/[salt]. You can find the pKa for propanoic acid in the data booklet.
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abstraction98
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#117
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#117
(Original post by phpurvis)
Need to know how much water they're dissolved in methinks.

Find out the number of moles of each substance by finding their relative formula masses first.

Then you'd use C = N/V to find the concentration, dividing the number of moles by the volume of water.

Once you have the concentration of each, use the following equation:

pH = pKa - log[acid/[salt]. You can find the pKa for propanoic acid in the data booklet.
Great, but the whole reason it's slightly tricky is that there is no volume of water given!
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Dan11
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#118
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#118
abstraction- what do u mean by let volume =v?
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Dan11
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#119
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#119
ahhhhh i get it
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phpurvis
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#120
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#120
(Original post by abstraction98)
Great, but the whole reason it's slightly tricky is that there is no volume of water given!
I don't get it then - help!
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